Stéphane’s Post for Sept. 08/10

A Tale of Two Raptors

At the station, this fall, we very frequently see Bald Eagles. It seems that at least 2 adults have adopted the area. It is always a sight to enjoy, but the presence of a top predator in an area is not just a thrill to birdwatchers. It sends ripples all throughout the natural world, some obvious, other more subtle.

For example, one morning, one adult Bald Eagle was seen trying to catch a cormorant. The cormorant only saved its life by frantically diving in the water and hoping the eagle, hovering above it, will lose patience, which it eventually did. However, every time a Bald Eagle flies by, all the cormorants resting on rocks in Wingfield Basin take flight and go out onto the water on a tight raft. The Bald Eagle is thus seen as a predator by the black fishing bird. It has indeed been shown that a Bald Eagle flying over a cormorant colony would send the adults off, leaving the nests, eggs, and young exposed to other predators, like ravens, gulls, and crows. So, maybe a solution to the alleged “over-abundance” of cormorants is simply more eagles!

An Eagle is also well capable of taking gulls, like the young Herring Gull we found half-eaten on the shore of Georgian Bay. Although we did not actually witnessed the kill this time, we strongly suspected the Bald Eagle as a culprit. Two ravens were enjoying the leftovers, which is another way the Eagle’s presence influences the intricate and complex web of life: providing food for other, “lesser”, beings. Common Ravens, though incredibly smart, are not strong enough to take down a fully-grown Herring Gull, but would certainly enjoy a free meal.

Other predators are present at Cabot Head, of course. One that breeds here every year is the Merlin; a turbo-fast bird, expert at catching birds on the wing! This time, though, it was a Monarch that the Merlin got, as observed by Matthias, a volunteer from Austria. However, the Merlin quickly let go, presumably knowing of the Monarch’s toxicity. You usually don’t have flashy colors when you’re so low on the food chain, unless you are confident of your toxins!

And today (September 8/10), another interesting interaction was witnessed by everyone here at the Cabot Head Research Station: A Merlin was mobbing and chasing an American Kestrel. The Merlin was just slightly bigger but was going on and on against the poor kestrel that the kestrel eventually let go of what it had in its talons. However, the Merlin was not the least interested in it and continued its mobbing! Was it territorial? Target practice? Finally, the kestrel got away and we saw it flying quickly, not without looking over shoulder, in case the temperamental Merlin was ready for another pass…

A proud member of the Canadian Migration Monitoring Network

The Cabot Head Research Station is one of 25 bird migration monitoring stations across Canada. Providing baseline information on avian populations by sampling migrants, by capture or observation, daily during migration contributes to our knowledge about bird populations and movement.